Low-level static lip force control does not alter vibrotactile detection thresholds in the human orofacial system

Mechanosensation associated with precise orofacial force regulation may contribute considerably to processes associated with perception, proprioception and sensorimotor control due to the direct coupling between orofacial skin and the underlying musculature. Recent investigations have demonstrated that dynamic, low-level lip force control is capable of modulating vibrotactile detection thresholds of the lips in a frequency-dependent manner. What is not known is whether the mode of motor control (static versus dynamic) may represent an important control variable in the expression of these perceptual threshold changes. The purpose of this study was to assess lower-lip (LL) vibratory detection thresholds from adult subjects during the simultaneous performance of a visually regulated, static lip motor control task. Vibrotactile inputs were delivered to the right LL vermilion at test frequencies of 5, 10, 50 and 150 Hz. Psychophysical detection was performed simultaneously during a no-force baseline condition and an active static force control task performed with the lip musculature. Subjects used their analog lip force signal to maintain a static lip force posture by visually tracking a steady-state force target calibrated to a 0.1 N load. Both signals were displayed in real time on a monitor. Results suggest that, unlike dynamic lip motor control, low-level, static lip force regulation is not effective in altering LL vibrotactile detection thresholds to any test frequency. These findings are discussed in relation to published reports of movement-related sensory gating in orofacial and limb systems and the possible significance this phenomenon may have for perception and proprioception in the orofacial system.